The first objective of this proposal is to demonstrate that breastfed preterm infants have earlier gut closure than formula fed infants as measured by markers of gut maturity, and that human milk and HMM derived TGFalpha and serum TGFalpha concentrations in neonates correlate with these markers. The second objective of this proposal is to delineate the role of human milk and HMM derived TGFalpha isoforms in gut maturation using an in vitro model, and to distinguish the biologic effect of TGFalpha from that of EGF.